3.1 Frontal cyclogenesis induced by the Arctic sea-ice retreat

Tuesday, 3 May 2011: 8:30 AM
Rooftop Ballroom (15th Floor) (Omni Parker House )
Jun Inoue, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan; and M. E. Hori

Direct observations of frontal cyclogenesis at the Arctic marginal ice zone were made during an Arctic cruise by the Japanese R/V Mirai in 24-25 September 2010. Intensive radiosonde and Doppler radar observations successfully acquired a life cycle of an extratropical cyclone from cyclogenesis to cycloysis.

During an incipient phase of cyclogenesis on 24 September, our Doppler radar detected cold and warm fronts characterized by intense convective clouds over the northeastern ice edge in the Beaufort Sea. After a passage of this surface cold front, the center of surface cyclone appeared, while in the northwest region of it a positive potential vorticity (PV) anomaly was approaching at the upper troposphere. This situation is likely a rapid cyclogenesis with a coupling process. After 18 hours, the warm and cold fronts distinctly separated at the south of the cyclone (frontal fracture), and then it developed into its T-bone phase. The radar detected a cumulus cloud streets within the cold air around the eastern side of the cyclone. Due to the intrusion of positive PV anomaly, tropopause dropped to 5-km level, resulting in cold dome. The developed surface cyclone moved relatively fast northeastward following an upper PV anomaly. Until 28 September, the ice-free Chukchi Sea was continuously covered with stratocumulus cloud streets induced by this cyclone, suggesting that strong air-sea heat transfer occurred during this event.

Revisit of an oceanic section before and after the cold-air outbreak induced by this cyclone showed 2 K decrease in water temperature at a sub-surface layer, which means that a large amount of heat flux was supplied to the atmosphere. Our observational results demonstrated that sea-ice distribution associated with recent rapid sea-ice retreat is substantially favorable to generation of an extratropical cyclone, accelerating the air-sea heat transfer and Arctic temperature amplification during winter.

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